That button is supposed to open Display preferences, but if your monitor isn't being detected properly I can see why it wouldn't. If it's a PowerMac that it's plugged into, I'd suggest shutting off the computer, unplugging it, and checking the video card to make sure that it's snugly in place (pull it and replace it, if you can) - be careful with the 'foot' lever! Then plug your machine/monitor back in and see if the display is properly recognized.

Thanks, Joe G4
Ive tried what you suggest but still doesnt open up prefs direct from the glow button..
I can go into screen prefs via the system prefs window but there isnt any slider to alt brightness, theres only options to change calibrartion.
Still stuck.
If all else fails I do have a PC screen (in my old G4) but the cable (plug into card) differs.

In order for the brightness controls to work, you need to connect the USB cable to the computer. If the cable is connected, then the display is probably malfunctioning.

Ive since went back and discovered that more info may help some to help:
I have the big encased plastic Display that cam with many G4s
Im running a 1.8Ghz G5 with 10.5.8 leopard
The display connector is of ADC type hence doesnt have any additional USB etc and it pulls the power from the Mac itself.

Problem:
The display is dim.
Cant find any controls to increase brightness, the icon on bottom left off screen doesnt trigger any controls.
There is no option to change brightness on the display prefs.

Last edited by stuartm; Feb 6, 2011 at 12:57 PM.
Reason: More info received